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Re: [Qemu-devel] [PATCH] qdev: Reset hotplugged devices

From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCH] qdev: Reset hotplugged devices
Date: Thu, 26 Aug 2010 08:25:36 -0500
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20100713 Lightning/1.0b1 Thunderbird/3.0.6

On 08/26/2010 08:15 AM, Avi Kivity wrote:
 On 08/25/2010 03:55 PM, Anthony Liguori wrote:

Maybe we can merge the patches.
As for your patch, I have some comment.
- bus itself may want its own handler. At lease pci bus needs it.
And propagating reset signal to children is up to the bus controller.

I disagree. Reset should be equivalent to power off + init and it's not something that can be selectively propagated.

Not all busses propagate reset - SCSI is an example (I think).

We're talking about cold reset vs. warm reset.

In the absence of passthrough, I'm struggling to see a useful use-case with warm reset. However, there are many useful things we can do assuming a cold reset (like MADV_DONTNEED memory on reboot).

That's not saying we shouldn't do a warm reset, but I'd like to see that as an incremental addition to what we have today (like introducing a propagating warm reset callback) and thinking through what the actual behavior should and shouldn't be.


Anthony Liguori

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